The patrol stumbled on the explosives late Saturday after “observing suspicious movement of approximately five persons” near the town of Khiam, eight kilometres (five miles) from the border with Israel, a statement said.
The peacekeeping force said it opened an investigation into “the precise nature of the explosives and the circumstances under which it was found,” noting that the find violates UN Security Council Resolution 1701.
“As the patrol approached the location, the group of unidentified persons fled the area in the cover of darkness,” the statement said, adding that UNIFIL peacekeepers found at the site “a significant quantity of explosives.”
“The presence of unauthorised explosives in the area constitutes a clear violation of UN Security Council resolution 1701 (2006)… and is a matter of serious concern,” the statement said.
Resolution 1701 ended a 2006 war between Israel and the Lebanese Shiite militant group Hezbollah, and calls for the dismantling and disarming of all militias operating in Lebanon.
Hezbollah has refused to heed the disarmament demand, however, arguing it needs to retain its arsenal for defence against Israel.
Lebanon also hosts a number of well-armed Palestinian factions that reject the peace process with Israel.
UNIFIL said it was cooperating with the Lebanese army to determine the nature of the explosives and “must await the findings of the investigation before we can make any final assessment and conclusion.”
The explosives have been handed over to the Lebanese army.
The mandate of UNIFIL, which has been in Lebanon since Israel first invaded the south 1978, was expanded when the resolution was passed after the 2006 war.
Over the past year, the peacekeepers have launched at least four investigations after rockets were fired at Israel from southern Lebanon.